1. Field of the Invention
The present invention relates to a picking device for a fluid jet loom and, more particularly, to a positive feed picking device provided with a positive feed mechanism for positively feeding a weft yarn for picking.
2. Description of the Prior Art
The main picking nozzle of a fluid jet loom needs to pick a weft yarn against a resistance against pulling out the weft yarn from a yarn measuring and storing device.
An invention intended to reduce the load on the main picking nozzle of a fluid jet loom is disclosed in Japanese laid-open patent application (Kokai) No. Sho 51-58563. According to this invention, a weft yarn is fed positively by a pair of rollers comprised of a movable roller and a fixed roller that rotates continuously during a picking cycle. The pair of rollers nip the weft yarn therebetween during a picking period and the movable roller separates from the other roller to stop feeding the weft yarn upon the completion of a picking operation. Although nothing concrete is mentioned in the invention about controlling the timing of separating the movable roller from the fixed roller, the time for separating the movable roller from the fixed roller can be determined on the basis of the angular position of the main shaft of the fluid jet loom because the movable roller is brought into contact with the fixed roller when the main shaft is at a picking starting angle. When the pair of rollers are controlled in such a manner, the rollers are unable to feed a set length of weft yarn and an insufficient length of weft yarn is fed if the rollers slip relative to each other, which reduces the rotational energy utilization efficiency.
If the time for separating the movable roller from the fixed roller is delayed, an excessive length of weft yarn is fed, thereby increasing the tension in a portion of the weft yarn extending between the yarn measuring and storing device and the pair of rollers, which is liable to cause yarn breakage.